1. Field of the Invention
The present invention relates to a television broadcast receiver for receiving terrestrial broadcasts.
2. Description of the Related Art
Conventionally, directional antennas such as a Yagi antenna are used to receive terrestrial broadcasts. A directional antenna has a high directivity to be able to receive a weak radio wave or signal. At the same time, the directional antenna has a drawback that it can receive only a radio wave coming from one direction. This is not a big problem in countries like Japan where many broadcast towers are concentrated in one location. However, in countries like the United States of America, there are many areas where broadcast towers spread around cities. If a directional antenna such as a Yagi antenna is used in such case, it may occur that the directional antenna cannot receive many broadcasts from broadcast towers even if the directional antenna is placed close to the broadcast towers.
In order to solve such problem, the EIA (Electronic Industries Association)-909 standard “Antenna Control Interface” was instituted, which provides a technology that a television broadcast receiver can control and change active receiving directions of the antenna. More specifically, it is a standard to connect, to a television (TV) broadcast receiver, a so-called smart antenna which is capable of changing active receiving directions, and to control the antenna by the TV broadcast receiver via a modular terminal. In the present specification, the two kinds of antennas are distinguished by referring to the directional antenna, such as the Yagi antenna, as a unidirectional antenna, and by referring to the antenna capable of changing its active receiving directions as a multi-directional antenna.
FIG. 7A is a schematic block diagram of an example of a conventional TV broadcast receiver 101 correctly or normally connected to a smart antenna 102 conforming to the EIA-909 standard. In order to connect the TV broadcast receiver 101 to the smart antenna 102, the TV broadcast receiver 101 has an RF terminal 111a connected via an RF cable 41 to an RF terminal 122b of an antenna controller 122 of the smart antenna 102, and also has a modular terminal 117 connected via a modular cable 42 to a modular terminal 122a of the antenna controller 122. In the case where the smart antenna 102 has an antenna unit 121 as a separate element from the antenna controller 122 as shown in FIG. 7A, an additional RF cable 43 is used to connect between the antenna unit 121 and an RF terminal 122c provided in the antenna controller 122 for antenna connection. The TV broadcast receiver 101 receives TV broadcast signals via the RF terminal 111a, and communicates e.g. control signals via the modular terminal 117. The antenna controller 122 receives control signals from the TV broadcast receiver 101 via the modular terminal 122a, and changes or switches active receiving directions of the antenna unit 121 on the basis of the thus received control signals.
In such antenna connection, correct connection of cables is important. For example, electric power for driving the antenna unit 121 and the antenna controller 122 of the smart antenna 102 is transferred along with the control signals to the antenna controller 122 via the modular cable 42, and is supplied to the antenna unit 121 via the RF cable 43. However, if a user makes a mistake and connects the RF cable 41 to the RF terminal 122c for antenna connection, and further connects the RF cable 43 to the RF terminal 122b for TV broadcast receiver connection as shown in FIG. 7B, it becomes impossible to supply electric power to the antenna unit 121 for switching between active receiving directions of the antenna unit 121 on the basis of the control signals.
Even if the user makes a mistake in connecting the RF cables 41 and 43 in the above-described way, however, it may be difficult for the user to be aware of the mistake in the connections, since it may be possible for the TV broadcast receiver 101 to receive a TV broadcast signal of a channel to be received in an active receiving direction of the antenna unit 121. Note in this connection that each of Japanese Registered Utility Model 3035217 and Japanese Laid-open Utility Model Publication Hei 10-302 discloses an example of an antenna device with an electric circuit designed to be able to detect connections between an antenna or the like and a controller or the like.
On the other hand, the EIA-909 standard provides a Mode A to enable one-way communication from a TV broadcast receiver to an antenna as well as a Mode B to enable two-way communication between a TV broadcast receiver and an antenna. A TV broadcast receiver for the Mode B can provide higher performance, using the two-way communication, by determining a specific protocol to be used between the TV broadcast receiver and the smart antenna. Note here that a TV broadcast receiver conforming to the EIA-909 standard can send such a control signal that allows a response signal to be sent back to the TV broadcast receiver if a smart antenna for the Mode B is connected to the TV broadcast receiver, without a response signal being sent back if a smart antenna for the Mode B is disconnected from or not connected to the TV broadcast receiver, so as to determine, based on the response signal, whether or not a smart antenna for the Mode B is connected thereto.
A conventional TV broadcast receiver, however, cannot determine whether or not a multi-directional antenna is correctly or normally connected thereto, although the TV broadcast receiver can determine whether it is connected to a multi-directional antenna capable of the one-way communication (smart antenna for the Mode A), or a multi-directional antenna capable of the two-way communication (smart antenna for the Mode B). Furthermore, the conventional TV broadcast receiver cannot determine whether or not the multi-directional antenna is adapted to a predetermined function which the TV broadcast receiver provides by using the two-way communication. Thus, a user cannot recognize whether a multi-directional antenna is correctly connected to a TV broadcast receiver, and cannot recognize whether the multi-directional antenna is adapted to a predetermined function provided by the TV broadcast receiver.